1. Field of the Inventions
The present inventions are generally related to image forming devices and, more specifically, image forming devices including reciprocating carriage and guide rail systems.
2. Description of the Related Art
Many image forming devices, such as printers, plotters, copiers and facsimile machines, include a printing component that is mounted on a reciprocating carriage. The carriage slides (or “scans”) back and forth on one or more cylindrical guide rails during an image formation procedure while the printing component forms an image, such as text or graphics, onto a substrate. Inkjet printers, for example, include one or more carriage mounted printhead cartridges (or “pens”) that are carried on a printer carriage. The printhead cartridges typically include a printhead with a plurality of ink ejecting nozzles. During a printing operation, the printer carriage will traverse back and forth over the surface of the print medium as the print medium is advanced in a direction transverse to that of the carriage. A controller causes the nozzles to eject drops of ink at times intended to result in the desired image.
There are six degrees of possible movement for any object—three linear directions (X, Y, Z) and three rotational directions (θX, θY, θZ). It is vitally important that printer carriages scan back and forth in a straight line. In order to insure linear movement, the printer carriages must be constrained in two linear and three rotational directions. Constraining movement in, for example, the Y, Z, θX, θY, and θZ-directions is desirable because it leaves the printer carriage free to move only in the X-direction.
Many conventional printer carriages include a pair of longitudinally spaced circular bushings with a slightly greater diameter than that of the guide rail which extends through the bushings. The bushings are mounted on one side of the carriage, while a single guide pin is mounted on the other side. The guide pin prevents rotational movement about the guide rail axis. It has been found that such an arrangement is less than optimal. In order to insure that the carriage does not move in a direction other than the X-direction as the printer carriage scans back and forth, the bushings must be sized within extremely tight tolerances and essentially perfectly aligned with one another. Because such tolerances and alignments are not economically viable, the bushings have been made slightly larger than the guide rails. This leads to the possibility of movement of the printer carriage in directions other than the X-direction in response to external forces. Such movement, which is in the Y and Z-directions, leads to vibration of the printer carriage, unpredictability of the carriage location, binding and, ultimately, to a reduction in print quality.
One proposed solution to this problem is illustrated in commonly assigned U.S. Pat. No. 5,366,305. Here, the top portions of the printer carriage bushings (when the carriage is in the horizontal operating orientation and the printing component is facing vertically downward) include respective pairs of circumferentially spaced planar surfaces that, under the force of gravity, rest on the guide rail and provide two spaced lines of contact. Both surfaces are arranged at 45 degrees relative to a horizontal plane extending through the guide rail axis. The carriage is also provided with an anti-rotation roller that rides on a flat surface. Such an arrangement provides two spaced lines of contact with the guide rail and prevents the movement in the Y and Z-directions associated with circular bushings.
Although the printer carriage disclosed in U.S. Pat. No. 5,366,305 is an improvement over those including circular bushings, the inventors herein have determined that such a system is inadequate in those instances where it is desirable to rotate the carriage about the θX axis to print in a direction other that vertically downward. For example, it may be desirable to rotate the printer carriage 90 degrees and mount the printer carriage such that the printing component is facing horizontally to print on the vertically extending side of a box. The planar portions of the bushings will not be on top when the carriage is rotated in this manner. The planar portions will be on one side of the guide rail. The guide rail will be in contact with the bushings at a point on one of the planar surfaces, which is arranged at 45 degrees, and with a vertically facing point on the bushing circular portion as gravity forces the bushings down against the guide rail. There will not be any constraint on the side of the bushings opposite the planar surfaces that are in contact with the guide rail. This leaves the printer carriage free to move in the Y-direction, thereby resulting in the aforementioned problems associated with movement in directions other than the X-direction.
The inventors have determined that one possible solution to the problems associated with mounting print carriages in a variety of orientations is to simply design and manufacture a special version of each print carriage for each particular orientation. This proposed solution is, however, untenable because of the manufacturing and inventory costs associated therewith.